Oxidation resistant refractory alloy



OXIDATEQN RESESTANT REFRACTORY ALLOY Lewis .1. lanes and Eugene Viainer,Cleveland, Ohio, as signers to Thompson Products, Inc., Cleveland, Ohio,a corporation of Ohio No Tra ning. Application May 14, 1951,

Serial No. 226,292

*7 Claims. (61-755176) The present invention relates to an oxidationresistant refractory metal alloy, particularly suited for use in hightemperature environments.

Recent developments in the field of aircraft engines, particularly inturbojet engines, have necessitated the provision of high temperaturealloys which can retain their hot strength characteristics even in thepresence of oxidizing and corrosive atmospheres.

One of the primary uses to which the alloys of the present invention canbe put is the manufacture of turbine buckets for jet turbine engines. Aturbine bucket will normally be exposed to temperatures in the rangefrom about 1600 F. to 2000 F. in the operation of the turbine engine,and the bucket must have suflicient strength, toughness, creepresistance, and resistance to the oxidizing gases present in the turbineengine to enable the bucket to opcrate efficiently without deformationor corrosion.

In addition to turbine buckets, articles produced from the alloys of thepresent invention may be employed under conditions of higher temperatureand lower stress than exist in a gas turbine bucket. One suchapplication occurs in nozzle diaphragm vanes in gas turbines which mustwithstand very severe conditions of temperature and thermal shock but ata relatively low stress.

One metal which exhibits excellent properties of strength, toughness,and creep resistance'atelevated temperatures is molybdenum. This metalcould be an extremely important raw material for jet engine manufacture,as deposits of molybdenum ores are plentiful in this country. The use ofpure, metallic molybdenum, however, in high temperature oxidizingatmospheres is not feasible because the molybdenum metal oxidizes ratherrapidly at temperatures even below the normal operating temperature ofthe gas turbine engine. At temperatures above 1,000 E, metallicmolybdenum oxidizes to form the trioxide of molybdenum, and thistrioxide sublirnes at a rapid rate as the temperature is increased.

We have now found that the hot strength characteristics of molybdenumcan be retained while at the same time increasing the oxidationresistance of the metal by alloying the metal with nickel and aluminum.The alloys of the present invention are refractory base alloys,

that is, they contain at least 50% by weight of molybdenum.

An object of the present invention is to provide a refractory metalalloy having good hot strength characteristics even in the presence ofoxidizing and corrosive atmospheres.

Another object of the present invention is to provide a molybdenum basealloy suitable for the manufacture of articles normally employed underconditions of high temperature and high stress.

Another object of the present invention is to provide a molybdenum basealloy whose forgeability characteristics can be varied by variation ofits composition.

Still another object of the present invention is to provide molybdenumbase alloys containing nickel and aluminum as primary components.

In general, the molybdenum alloys of the present invention containnickel in amounts up to 25% by weight, and aluminum in amounts up to byweight, the weight ratio between the nickel and aluminum contents in thealloy preferably being between values of 6 to 1 and to 1.

We have also found that the oxidation resistance of such molybdenum basealloys can be increased by the addition of substantial amounts ofchromium. The increase in oxidation resistance, however, through theaddition of States Patent 50 2,698,786 P tented lent b,

chromium, decreases the forgeability of the alloy. 0nsequently, Wherethe alloymust be subjected to a subsequent forging operation, thechromium content is pref: erably held to a minimum, or completelyeliminated. (in the other hand, substantial amounts of chromium, up to.25 by weight can be included in the alloys where the forgeability of thealloy is unimportant. This is the case where the articles are fabricatedfrom the alloy by powder metallurgy techniques.

In addition to the above components, the alloys of the present inventionmay contain minor percentages of ele: ments which stabilize andstrengthen the alloy. Such elements include cobalt, manganese, silicon,titantium, zirconium, and boron. In the alloys of the present inven:tion, the total addition of such elements should not ex-, ceed about 3%by weight of the alloy.

The alloys of the present invention fall within the following ranges ofcomposition, excepting the possible a'ddi, tion of minor amounts ofstabilizing and strengthening 20 elements:

Table I Ni 8-25 by weight. Al l-5% by weight. 9 Cr -7--- og- Balance (ete. $t5Q%)- When relatively small amounts of chromium are added thenickel content should be comparatively high. The following tableillustrates ranges for contents of the 0 various elements whererelatively small amounts of chro:

miuin are used:

Table II Ni 10-25% by weight. Al 15% by weight. Cr 4-5% by weight. MoBalance.

As larger amounts of chromium are added, to increase the oxidationresistance of the alloy, the average nickel 40 content is decreased fromthe range shown in the previous table, as illustrated in the following.table:'

Table Ill Ni 818% by weight. Al 1-3% by weight. Cr 20-25% by weight.

Mo Balance.

Where forgeability is an important consideration, the chromium contentof the alloy is held to a minimum, or eliminated altogether. Onespecific alloy composition which has good oxidation resistance, whilestill having a fair degree of forgeability is the following:

Table IV Ni 17.3% by weight. ",5 Al 2.7% by weight.

Mo Balance.

Other typical alloys within the scope of the present invention,containing varying amounts of chromium and nickel are tabulated below:

Table V Ni 15 20 10 A1 2 3 1 3 2 20 Balance Balance Balance Aspreviously mentioned, the alloys of the present invention may alsocontain small amounts, up to about 3%, of stabilizing and strengtheningelements. For example the composition listed in Table IV can be modifiedby the addition of the stabilizing elements in the following Theforegoing alloys are all characterized by good oxidation resistance, andgood high temperature properties, while still retaining the refractoryproperties of the molybdenum base. One of the features of the alloys ofthe invention is the fact that their forgeability characteristics can bechanged by the control of the chromium content, alloys of the presentinvention will find extensive use wherever a material having good hotstrength characteristics and resistance to oxidation is required. Themolybdenum alloys of the present invention can be used at temperaturesfar exceeding those of which molybdenum itself can be effectivelyutilized.

It will be appreciated that various modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention.

We claim as our invention:

1. An oxidation resistant alloy having the following composition:

Ni 8-25% by weight. Al 1-5% by weight. Cr 0-25% by weight. Mo Balance(at least 50%).

Ni 10-25% by weight. Al 1-5% by weight. Cr 4-5% by weight. Mo Balance.

the Mo, Ni, Al and Cr contents totalling at least 97% by weight of saidalloy.

3. An oxidation resistant molybdenum base alloy having the followingcomposition:

N 53-18% by weight. Al 13% by weight. Cr 20-25% by weight. Mo Balance.

the Mo, Ni, Al and Cr contents totalling at least 97% by weight of saidalloy.

4. An oxidation resistant molybdenum base alloy having the followingcomposition:

N 17.3% by weight.

4 A 2.7% by weight. Mo Balance.

5. An oxidation resistant alloy having the following composition:

Ni 8-25 weight per cent. Al 1-5 weight per cent. Mo Balance.

wherein the NizAl weight ratio is from 6:1 to 10:1, the Mo, Ni and Alcontents totalling at least 97% by weight of said alloy.

6. An oxidation resistant alloy having the following composition:

Ni 8-18 weight per cent. Al 1-3 weight per cent. Cr 20-25 weight percent. Mo Balance.

wherein the NizAl weight ratio is from 6:1 to 10:1, the Mo, Ni, Al andCr contents totalling at least 97% by weight of said alloy.

7. An oxidation resistant alloy having the following composition:

OTHER REFERENCES Transactions of Amer. Soc. for Metals, vol. 43 (1951),pages 193-225.

Transactions of A. S. M. B, vol. 73 (1951), pages 723-732.

1. AN OXIDATION RESISTANT ALLOY HAVING THE FOLLOWING COMPOSITION:NI------------------------------- 8-25% BY WEIGHT.AL-------------------------1-5% BY WEIGHT.CR--------------------------0-25% BY WEIGHT. MO-------------------------BALANCE (AT LEAST 50%). THE MO, NI, AL AND CR CONTENTS TOTALLING ATLEAST 97% BY WEIGHT OF SAID ALLOY.